In the construction of such roadways a deck is laid discontinuously with openings running across the roadway to permit movement between adjacent parts of the bridge. These movements can involve considerable displacements longitudinally of the roadway due to expansion and contraction of the bridge, and also can involve a flexing or bending at the joint. Their effect on the upper layers of the roadway must be reduced as much as possible to preserve these continuous upper layers from unnecessary movement and their subsequent deterioration, and this, as well bridging the gaps formed by the discontinuities in the deck, is the function of an expansion joint.
The expansion joint is laid on top of the deck to bridge the opening between adjacent decks. In addition to absorbing the forces between the deck parts due to expansion of those deck parts without being damaged by these forces or transmitting them harmfully to either the roadway surface or the supporting deck part, buried expansion joints should provide an adequate seal against surface water and debris penetrating the openings between the decks of the bridge.
Ideally, buried bridge expansion joints should:
(A) PROVIDE A SAFE SMOOTH RIDE FOR VEHICLES OVER THE JOINT;
(B) BE CAPABLE OF ABSORBING IMPACT FORCES WITHOUT TRANSMITTING THESE FORCES HARMFULLY TO THE BRIDGE DECKS AND ROADWAY SURFACE,
(C) BE CAPABLE OF SUPPORTING THE HEAVIEST TRAFFIC LOADS OVER THE JOINT WITHOUT UNACCEPTABLE VERTICAL DEFLECTION OF THE ROADWAY SURFACE, THEREBY PROVIDING A DURABLE FRACTURE FREE WEARING SURFACE TO THE ROAD OVER THE EXPANSION JOINT,
(D) BE CAPABLE OF ACCOMMODATING AT LOW STRESS VALUES ALL THE HORIZONTAL AND SKEW MOVEMENTS THAT WILL BE EXPERIENCED BY THE BRIDGE DECKS FOR WHICH THE EXPANSION JOINT IS DESIGNED,
(E) BE CAPABLE OF ACCOMMODATING DECK ROTATIONS WITHOUT SEVERE ROAD SURFACE DEFLECTION,
(F) BE EASY TO INSTALL AND BE CAPABLE OF ACCOMMODATING A DEGREE OF MISALIGNMENT BETWEEN THE ADJACENT DECKS,
(G) BE CAPABLE OF PROVIDING A DURABLE AND EFFECTIVE SEAL THROUGHOUT THE BRIDGE JOINT, TO THEREBY PREVENT THE PENETRATION OF SURFACE WATER AND DEBRIS THROUGH THE JOINT, AND CONSEQUENTLY ELIMINATE THE NECESSITY OF SUPPLEMENTARY DRAIN SYSTEMS UNDER THE EXPANSION JOINT.
Over the past years many designs of buried expansion joints have been applied to accommodate the movements that occur in civil engineering structures, but practically all have failed to be satisfactory either from the point of view of durability or of ease of laying or both. A buried expansion joint which consisted of a metallic plate laid over the gap has particularly proved unsatisfactory as requiring great accuracy in laying (otherwise it will rock) and as being unable to accommodate the torsional forces which occur between adjacent deck parts during passage of vehicles. A buried expansion joint of very stiff elastomeric material comprising an elongated main portion generally rectangular in cross-section and consisting of a central bridging portion integral with a pair of lateral side limbs which are divided from the bridging portion by longitudinally extending voids and/or cavities which permit lateral expansion or contraction of the bridging portion to accommodate relative displacement of the roadway sections is disclosed in German patent application No. P25 20 521.4. The expansion joint disclosed in P25 20 521.4 includes a flashing, also of rubber, which extends over the upper surface of the elongated main portion, down its sides and along the surfaces of the decking adjacent the main portion to which it is attached by layers of adhesive bedding.
The flashing caters for tension movements and also provides a waterproof cover over the extension gap.
A debonding layer of aluminium faced sheet is laid above the expansion joint and extends for some distance on either side thereof to spread any extension over a considerable length of the surfacing. Buried expansion joints are assembled as they are laid and a construction, such as disclosed in P25 20 541.4 involving the separate positioning and securing of flashing and main portion, takes considerable time, and hence expense, to lay. The separate manufacture of two distinct elements also involves a cost disadvantage.